1. Field of the Invention
The present invention relates to a cap device having a torque mechanism for sealing a tank opening with a rotational torque of a predetermined level.
2. Description of the Related Art
A known fuel cap for an automobile fuel tank is disclosed in, for example, JP No. 2000-344266A. FIG. 17 is a decomposed perspective view showing a prior art torque mechanism 130 of a conventional fuel cap 100. The fuel cap 100 of FIG. 17 mainly has a casing main body 110, a cover 120 with a handle for rotational operations, and the torque mechanism 130. The torque mechanism 130 includes a handle engagement element 122 formed on the cover 120, a torque plate 140 having cantilevered torque arms 142 with torque engagement projections 142a, and a spring 132. In the case of rotation of the cover 120 in a closing direction, a rotational torque exceeding a predetermined level releases the engagement of the handle engagement element 122 with the torque engagement projections 142a to give a click. In the case of rotation of the cover 120 in an opening direction, on the other hand, the casing main body 110 rotates integrally with the cover 120 to open the fuel cap 100.
In the closing operation of the fuel cap 100, a click is given when the handle engagement element 122 rides over the torque engagement projections 142a of the torque plate 140. This proves that the fuel cap 100 is sealed with a substantially constant rotational torque of the predetermined level, regardless of the elasticity of a gasket.
The torque plate 140 having the torque arm 142 is formed by injection molding of resin. The long torque arm 142, however, tends to have varying dimensions, due to molding strain. Even slight change of the dimensions may result in a significant variation in rotational torque in the closing direction.